U.S. patent number 4,783,252 [Application Number 07/020,364] was granted by the patent office on 1988-11-08 for lateral indicator sensor.
This patent grant is currently assigned to Rosemount Inc.. Invention is credited to Barry W. Benton.
United States Patent |
4,783,252 |
Benton |
November 8, 1988 |
Lateral indicator sensor
Abstract
An electrochemical sensor for measuring an electrochemical
parameter such as pH in a flowing liquid has a housing with a
lateral cutout or indentation. An indicator electrode and a
reference junction extend into the indentation from opposite sides
so that they are facing one another and are axially aligned along a
common longitudinal axis which is generally perpendicular to the
flow of liquid.
Inventors: |
Benton; Barry W. (Orange,
CA) |
Assignee: |
Rosemount Inc. (Eden Prairie,
MN)
|
Family
ID: |
21798229 |
Appl.
No.: |
07/020,364 |
Filed: |
March 2, 1987 |
Current U.S.
Class: |
204/416; 204/400;
204/409; 204/420; 204/435 |
Current CPC
Class: |
G01N
27/283 (20130101) |
Current International
Class: |
G01N
27/28 (20060101); G01N 027/46 () |
Field of
Search: |
;204/415,416-420,400,409,435 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Abstract of Pfaudler-Werke AG British Pat. GB 1596-117, Scientific
Instrumentation, D34, p. 31. .
"pH and ORP Systems", Bulletin 101, pp. 7-8, Control Data
Corporation. .
Brochure: "Die Neue Generation", Conducta Brochure. .
Brochure: "Insertion/Submersion pH Sensor-Model PHS17",
Elector-Chemical Devices, Inc. .
Brochure: "pH/ORP Insertion Probe Mounting Assembly", Great Lakes
Instruments, Inc. .
Brochure: "Insertion Probe 768-35 and 769-35", Ingold Electronics
Inc. .
Brochure: "Model 520 Series pH/Redox Sensor-Transmitter", Lakewood
Instruments, Inc. .
Brochure: "7774 Removable Type pH Mounting for General Purpose and
Sterilizable Meredian Electrodes", L & N Inc. .
Brochure: "Insertion/Submersion pH Sensor-Model 916", Sensor
Technology, Inc. .
Brochure: "MK 319 Wet Tap Assembly", Signet Scientific, Inc. .
Brochure: "pH/ORP Sensors", TBI, Inc. .
Brochure: "Mark VII Insertion Sensors", Van London Company, Inc.
.
Brochure: "Insertable Flat Surface Combination pH Electrode",
Sensorex , Inc. Bulletin 410..
|
Primary Examiner: Tung; T.
Attorney, Agent or Firm: Kinney & Lange
Claims
What is claimed is:
1. A sensor for sensing an electrochemical parameter of a flowing
process material and providing an output representative of the
parameter, the sensor comprising:
a sensor body having an indentation forming an indentation surface
recessed from a side surface of the sensor body which opens to
receive a portion of the process material; and
a plurality of electrodes extending from the indentation surface
into the indentation to form a plurality of electrode surfaces
spaced away from the indentation surface for contacting the process
material in the indentation.
2. The sensor of claim 1 wherein the sensor body has the side
surface disposed to face downstream in the flowing process
material; and wherein the indentation opens downstream such that
the body shields the electrodes from suspended particles in the
flowing process material.
3. The sensor of claim 1 wherein the sensor body has the side
surface disposed to face upstream in the flowing process material
and the indentation opens upstream such that the electrodes receive
an increased flow of the process material for cleaning the
electrodes.
4. The sensor of claim 1 wherein the sensor body comprises an
elongated probe for extending into a region of flowing process
material.
5. The sensor of claim 4 wherein a first electrode of the plurality
of electrodes comprises a reference junction electrode.
6. The sensor of claim 5 wherein a second electrode of the
plurality of electrodes comprises a species selective
electrode.
7. The sensor of claim 6 wherein the species selective electrode is
pH sensitive.
8. The sensor of claim 4 wherein the side surface of the probe is
substantially cylindrical for insertion through a ball valve into
the flowing process material.
9. A sensor probe insertable into a flowing process material, the
sensor probe comprising:
a probe body having a distal end for insertion in the flowing
process material, a proximal end disposed away from the distal end
and connected by a side wall having an indentation forming an
indentation surface therein which is spaced away from the distal
end;
first electrode means disposed in the probe body and extending
outwardly from the indentation surface into the indentation;
and
second electrode means spaced away from the first electrode means
and having a reservoir of electrolyte in the probe body and
junction means permeable to the electrolyte coupled between the
reservoir and the indentation for electrochemically coupling to the
process material, the junction means protruding into the
indentation.
10. The probe of claim 9 wherein the first electrode means has an
active region disposed opposite the junction means in the
indentation.
11. The probe of claim 9 further comprising means coupled to the
reservoir for controlling pressure of the electrolyte.
12. The probe of claim 11 wherein the means for controlling
pressure comprise a diaphragm disposed in the probe body for
coupling pressure from the process material to the electrolyte.
13. The probe of claim 11 wherein the means for controlling
pressure comprise means disposed in the probe body for producing a
force and a plunger for transferring the force to the
electrolyte.
14. The probe of claim 13 wherein the means for producing a force
comprise a coil spring.
15. The probe of claim 13 wherein the means for producing a force
comprise compressed gas.
16. The probe of claim 9 further comprising a shroud positioned on
the side wall and having an aperture therethrough which is
positionable with respect to the indentation for controlling
exposure of the first and second electrode means to the process
material.
17. A sensor comprising:
an elongated housing having a lateral cutout in a side wall;
indicator electrode means supported by the housing and having an
active region protruding into the cutout; and
reference electrode means supported by the housing and having an
active region protruding into the cutout opposite and spaced from
the indicator electrode active regions, the active regions being
essentially aligned along a common longitudinal axis which is
generally parallel to an elongated direction of the housing.
18. The sensor of claim 17 wherein the housing has a cavity
therein; and wherein the reference electrode means includes an
electrolyte within the cavity, and means for providing
electrochemical contact with the electrolyte.
19. The sensor of claim 18 wherein the means for providing
electrochemical contact includes a reference wire, a reference
solution, and a permeable junction extending between the reference
solution and the electrolyte.
20. The sensor of claim 17 wherein the housing has a main bore and
a passage extending between the main bore and the cutout; and
wherein the indicator electrode means extends from the main bore
through the passage into the cutout.
21. The sensor of claim 17 and further comprising a shroud mounted
over and movable with respect to the housing, the shroud having an
aperture which is positionable with respect to the cutout by
relative movement between the shroud and the housing.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to electrochemical sensors, and in particular
to a sensor for measuring electrochemical activity of a selected
species in a flowing material.
2. Description of the Prior Art
A wide variety of electrochemical sensors have been developed and
used for industrial applications. For example, pH sensors have been
used for many years and commonly make use of an indicator electrode
and a reference electrode. The indicator electrode is commonly a pH
sensitive glass member which contains a suitable electrolyte and in
which is immersed an internal reference. The reference electrode
commonly contains a reference solution (an electrolyte) and an
internal reference. Unlike the indicator electrode, the reference
electrode also includes some form of junction for establishing
contact between its internal electrolyte and the liquid being
tested. The sensor output signal is in the form of a potential
between the indicator electrode and the reference electrode.
When this type of sensor is used to measure electrochemical
activity in a flowing liquid, there are a number of potential
sources of inaccuracies and problems which are encountered. In
particular, streaming potentials caused by the flow of fluid past
the indicator electrode and reference junction and stray electric
current can both result in inaccurate potentials being produced.
Sensors of this type have generally been rather fragile, and the
insertion of the sensor through a sometimes obstructed passage into
the fluid, and the possible presence of stream debris, can result
in cracking or breaking of the indicator electrode. Fouling of the
sensor by debris contained in the liquid stream also presents a
problem with prior art electrodes.
SUMMARY OF THE INVENTION
The lateral indicator sensor of the present invention is an
electrochemical sensor having an indicator electrode and a
reference electrode which are supported by a housing in a
relationship in which the active areas of the indicator electrode
and reference electrode face one another and are closely spaced
from one another. The housing has an indentation or cutout in a
major side surface, and the active portions of the indicator
electrode and reference electrode extend into the indentation from
opposite sides so that they are closely spaced and axially aligned
along a common longitudinal axis which is generally transverse to
the direction of flow.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are side and rear views, respectively, of a
preferred embodiment of the lateral indicator sensor of the present
invention.
FIG. 2 is a sectional view, along section 2--2 of FIG. 1B.
FIG. 3A shows the insertion of the lateral indicator sensor into a
process pipe in which the passage for the sensor is blocked by a
closed valve.
FIG. 3B shows the lateral indicator sensor in position in the
process pipe, and shows the flow of liquid with debris in the
process pipe.
FIGS. 4A and 4B are perspective views of the lateral indicator
sensor of the present invention and a prior art electrode with
associated guard, respectively.
FIG. 5A and 5B show flow of liquid past the indicator electrode
with two different orientations of the lateral indicator sensor
with respect to the liquid flow direction.
FIGS. 6-9 show other embodiments of the reference electrode of the
lateral indicator sensor of the present invention.
FIGS. 10A and 10B are perspective views showing the lateral
indicator sensor of the present invention in conjunction with an
outer housing or sheath.
FIG. 11 shows another embodiment of the lateral indicator sensor of
the present invention having a double junction reference
electrode.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As illustrated in FIGS. 1A, 1B and 2, sensor 10 of the present
invention has an elongated housing or body 12 with a lateral cutout
or indentation 14. Projecting into indentation 14 from opposite
directions are portions of indicator electrode 16 and reference
electrode 18. Electrodes 16 and 18 are positioned along a common
longitudinal axis 20 which is generally parallel to the
longitudinal axis (not shown) of housing 12 and generally
perpendicular to the direction of fluid or material flow, as
indicated by arrow 22.
As best shown in FIG. 2, indicator electrode 16 is a generally
cylindrical electrode, such as a pH sensing glass electrode having
a main body 24 with an active region 26 at one end and a wire 28
extending from its opposite end. Indicator electrode 16 extends
from main bore 29 of housing 12 through passage 29A so that active
region 26 is positioned to be exposed to fluid within indentation
or cutout 14.
Reference electrode 18 includes a reference wire 30 which extends
through main bore 29 and passage 29B and into cavity 32. An
electrolyte, such as a reference solution 33, fills cavity 32.
Reference junction 34 has one end within cavity 32 and its opposite
end extending into cutout region 14. Reference junction 34 is
axially aligned with indicator electrode 16 and is positioned in
close proximity to active area 26. Plug 36 closes cavity 32.
As liquid flows past sensor 10, some of the liquid contacts active
area 26 and reference junction 34 within cutout region 14. Because
of the ion selective characteristics of electrode 16, a potential
difference is produced between indicator electrode wire 28 and
reference wire 30. This potential, which is supplied to signal
measuring circuitry (not shown), is a function of concentration of
ions in the vicinity of active region 26 and reference junction
34.
As shown in FIG. 1A, the sensor 10 of the present invention is
preferably positioned so that lateral cutout 14 is on the
downstream side with respect to fluid flow. As a result, housing 12
partially shields active electrode 16 and reference electrode 18
from direct impingement of fluid and particles flowing in the
direction designated by arrow 22.
The positioning of reference junction 34 and indicator electrode
active region 26 along common longitudinal axis 20 creates a
central current path between the two electrodes. The close
proximity of active region 26 and the distal end of reference
junction 34 provides a very short current path between reference
electrode 18 and indicator electrode 16. Cutout region 14 ensures a
stable current path with high electrolyte concentration in the
proximity of indicator electrode 16 and reference electrode 18.
The proximity of active region 26 to reference junction 34 and
their common longitudinal axis reduces the effect of streaming
potentials. The common longitudinal axis 20 also reduces the effect
of stream direction on sensor output. By locating lateral cutout 14
on the downstream side of sensor 10, high flow rate stream
potentials are reduced because active region 26 and reference
junction 34 are in a low flow rate area.
In prior art systems, in which the indicator and reference
electrodes are not so closely spaced and aligned, stray current can
produce a large potential difference error between the two
electrodes. With the present invention, the proximity of active
region 26 to reference junction 34, and their common longitudinal
axis helps to reduce the potential errors caused by stray
electrical current.
The proximity of active region 26 and reference junction 34 along
common longitudinal axis 20 tends to minimize the resistance of the
current path between the reference and indicator electrodes 18 and
16. As discussed previously, locating lateral cutout 14 on the
downstream side of sensor 10 maximizes the concentration of
reference electrolyte at the indicator electrode in the low flow
rate area, thus reducing the current path resistance in high flow
rate streams. This is particularly important when measuring pH in
high purity water.
Other important advantages of the sensor of the present invention
are ilustrated in FIGS. 3A and 3B, where sensor 10 is a replaceable
sensor cartridge mounted on the distal end of a probe insertion
shaft 39. As shown in FIG. 3A, sensor 10 is being inserted through
pipe 40 into process pipe 42. During insertion, sensor 10 will
encounter an obstruction (in this case closed ball valve 44).
Unlike prior art sensors in which the indicator electrode is
mounted at the end of the sensor, the present invention ensures
that the point of impact between sensor 10 and the obstruction is
at a location away from indicator electrode 16 and particularly its
active area 26. By locating active region 26 and reference junction
34 in lateral cutout 14, sensor 10 guards indicator electrode 16
from damage or breakage due to mishandling, obstructed insertion,
or debris contained in the process flow.
FIG. 3B shows sensor 10 inserted through pipe 40 and open ball
valve 44 into process pipe 42. The direction of flow, as indicated
by arrow 46 in FIG. 3B, carries the liquid 48 and debris 50 past
the distal end of sensor 10. By locating lateral cutout 14 on the
downstream side, housing 12 protects indicator electrode from
damage caused by flowing debris 50.
FIGS. 4A and 4B illustrate another important advantage of the
present invention. FIG. 4A is a perspective view of sensor 10,
while FIG. 4B illustrates a prior art sensor 60. As shown in FIG.
4B, sensor 60 includes an indicator electrode 62 carried by housing
64. At the distal end of housing 64 are a plurality of posts 66
which form a guard around the active area of indicator electrode
62. Guard posts 66 protect the active regions of electrode 62
against damage, particularly in the case of an obstructed insertion
like that illustrated in FIG. 3A.
The disadvantage of the prior art sensor 60 as illustrated in FIG.
4B is that the guard posts 66 project out from body 64. As a
result, they provide projections on which fibrous material carried
in the process liquid can be tangled or caught. As a result, guard
posts 66 can accumulate material which eventually fouls sensor
60.
With sensor 10 of the present invention, on the other hand, active
region 26 of indicator electrode 16 is protected by being
positioned within lateral cutout 14. No projections are required in
order to provide protection against mishandling or damage caused by
obstructions during insertion, and therefore there are no
projections to interrupt free flow. This reduces the tendency of
fouling caused by process stream debris.
Another advantage of the sensor 10 of the present invention is that
by rotating sensor 10 the orientation of cutout region 14 and
electrodes 16 and 18 with respect to the process stream can be
changed. FIGS. 5A and 5B illustrate two different orientations of
lateral cutout 14 which result in different fluid flow patterns
past active region 26 of indicator electrode 16. In FIG. 5A,
lateral cutout 14 has been rotated so that it is at least partially
facing upstream. This results in an increased flow rate past active
region 26 of indicator electrode 16. This increase in flow rate can
be used to provide a scouring action.
In FIG. 5B, lateral cutout 14 is positioned on the downstream side
of flow, so that sensor housing 12 acts as a bluff body to produce
vortices and turbulent flow around active region 26. This can also
be used to reduce the undesired precipitation in active region
26.
One problem encountered with electrochemical sensors having a
reference which includes a reference junction is that changes in
the pressure of the liquid being sensed relative to the reference
solution can cause a loss of reference solution through the
reference junction, or the migration in and contamination of the
reference solution by the liquid being tested. FIGS. 6-9 illustrate
four different embodiments of the reference electrode 18 of sensor
10 which are concerned with shifting junction potentials and loss
of reference solution due to fluctuating stream pressure. In each
of FIGS. 6-9, similar elements from FIGS. 1A, 1B and 2 are
designated with similar reference numerals.
In FIG. 6, plug 36 shown in FIG. 2 has been replaced by a flexible
diaphragm 70. Diaphragm 70 is exposed to the external fluid
pressure and transmits that fluid pressure to reference solution
33. Reference junction 34 is also exposed to the stream fluid
pressure, so that the internal and external pressures across
reference junction 34 are equalized. This eliminates reference
solution loss which would otherwise be caused by a pressure
differential.
In FIG. 7, plug 36 has been replaced by plunger 80, spring 82 and
plug 84 (which has a vent 86). In the embodiment shown in FIG. 7,
therefore, force is being applied to reference solution 33 by an
energized plunger 80 to maintain reference solution pressure above
stream pressure. This ensures a consistent junction solution and
concentration. Plunger 80 is energized by bias spring 82 (which is
partially under compression) and by fluid pressure of the stream,
which is transmitted to the backside of plunger 80 through vent
86.
FIG. 8 shows another embodiment in which plunger 90 is located
within chamber 32. A high pressure gas fills the portion of cavity
32A between the back side of plunger 90 and plug 36. This gas
pressure is at a pressure which is higher than the stream fluid
pressure. The result is that reference solution 33 is maintained
under a consistent pressure, but one which is not relative to
stream pressure.
FIG. 9 shows still another embodiment in which plug 100 at one end
of cavity 32 contains a threaded passage 102 in which removable
plug 104 is threaded. Cavity 32 can be refilled with reference
solution by removing plug 104 from passage 102.
FIGS. 10A and 10B show another embodiment of the present invention,
in which variable guarding of active area 26 of indicator electrode
16 is provided. In this embodiment, an outer housing or shroud 110
is positioned over housing 12 of sensor 10. Shroud 110 has a
lateral cutout 112 which is positionable with respect to lateral
cutout 14 by relative movement of housing 12 and shroud 110.
In FIG. 10B, shroud cutout 112 has been rotated 90.degree. with
respect to sensor lateral cutout 14. A greater amount of guarding
of electrode active area 26 can be achieved by rotating shroud 112
in the counterclockwise direction shown in FIG. 10B relative to
housing 12. Conversely, a lesser extent of guarding can be achieved
by rotating shroud 110 in a clockwise direction relative to housing
12.
Although cutout 112 illustrated in FIGS. 10A and 10B is of the same
general configuration as lateral cutout 14, in other embodiments
the configuration of cutout 112 and cutout 14 can be different to
enhance the guarding action.
Still another advantage which can be achieved is electrical
shielding from stray currents in the process fluid by shroud 110.
This requires that shroud 110 be an electrically conductive
material.
FIG. 11 shows another embodiment of sensor 10 in which reference
wire 30 has been replaced with another reference electrode 120 to
produce a double junction reference electrode. Reference electrode
120 includes a housing 122 having a junction 124 at one end which
is exposed to the interior of cavity 32 and thus to electrolyte
solution 125. The opposite end of junction 124 is exposed to second
reference solution 126 in cavity 128 of housing 122. Reference wire
130 has one end located within cavity 128 and its opposite end
extending out to provide electrical connection to sensing circuitry
(not shown).
Although the present invention has been described with reference to
preferred embodiments, workers skilled in the art will recognize
that changes may be made in form and detail without departing from
the spirit and scope of the invention. For example, although the
present invention is ideally suited to glass pH electrodes, it is
also applicable to other sensors using different indicator
electrodes, such as glass ion-selective electrodes, solid state
ion-selective or pH electrodes, and indicator electrodes using
permeable or semi-permeable membranes. Similarly, other reference
electrodes, including those using a solid electrolyte, can also be
used.
* * * * *